WASHINGTON (AP) — As a candidate, Barack Obama vowed to bring a different, better kind of leadership to the dysfunctional capital. He’d make government more efficient, accountable and transparent. He’d rise above the “small-ball” nature of doing business. And he’d work with Republicans to break Washington paralysis.

You can trust me, Obama said back in 2008. And — for a while, at least — a good piece of the country did.

But with big promises often come big failures — and the potential for big hits to the one thing that can make or break a presidency: credibility.

A series of mounting controversies is exposing both the risks of political promise-making and the limits of national-level governing while undercutting the core assurance Obama made from the outset: that he and his administration would behave differently.

The latest: the government’s acknowledgement that, in a holdover from the Bush administration and with a bipartisan Congress’ approval and a secret court’s authorization, it was siphoning the phone records of millions of American citizens in a massive data-collection effort officials say was meant to protect the nation from terrorism. This came after the disclosure that the government was snooping on journalists.

Also, the IRS’ improper targeting of conservative groups for extra scrutiny as they sought tax-exempt status has spiraled into a wholesale examination of the agency, including the finding that it spent $49 million in taxpayer money on 225 employee conferences over the past three years.

At the same time, Obama’s immigration reform agenda is hardly a sure thing on Capitol Hill, and debate starting this week on the Senate floor is certain to show deep divisions over it. Gun control legislation is all but dead. And he’s barely speaking to Republicans who control the House, much less working with them on a top priority: tax reform.

Even Democrats are warning that more angst may be ahead as the government steps up its efforts to implement Obama’s extraordinarily expensive, deeply unpopular health care law.

Collectively, the issues call into question not only whether the nation’s government can be trusted but also whether the leadership itself can. All of this has Obama on the verge of losing the already waning faith of the American people. And without their confidence, it’s really difficult for presidents to get anything done — particularly those in the second term of a presidency and inching toward lame-duck status.

The ramifications stretch beyond the White House. If enough Americans lose faith in Obama, he will lack strong coattails come next fall’s congressional elections. Big losses in those races will make it harder for the Democratic presidential nominee in 2016, especially if it’s Hillary Rodham Clinton, to run as an extension of Obama’s presidency and convince the American public to give Democrats another four years.

Obama seemed to recognize this last week. He emphasized to anxious Americans that the other two branches of government were as responsible as the White House for signing off on the vast data-gathering program.

“We’ve got congressional oversight and judicial oversight,” Obama said. “And if people can’t trust not only the executive branch but also don’t trust Congress and don’t trust federal judges to make sure that we’re abiding by the Constitution, due process and rule of law, then we’re going to have some problems here.”

The government is an enormous operation, and it’s unrealistic to think it will operate smoothly all of the time. But, as the head of it, Obama faces the reality of all of his successors: The buck stops with him.

If the controversies drag on, morale across America could end up taking a huge hit, just when the mood seems to be improving along with an economic uptick. Or, Americans could end up buying Obama’s arguments that safety sometimes trumps privacy, that his administration is taking action on the IRS, and that he’s doing the best he can to forge bipartisan compromise when Republicans are obstructing progress.

Every president faces the predicament of overpromising. Often the gap can be chalked up to the difference between campaigning and governing, between rhetoric and reality. As with past presidents, people desperate to turn the page on the previous administration voted for the Obama they wanted and now are grappling with the Obama they got.

From the start of his career, Obama tried to sculpt an almost nonpartisan persona as he spoke of bridging divides and rejecting politics as usual. He attracted scores of supporters from across the ideological spectrum with his promises to behave differently. And they largely believed what he said.

Back then, he held an advantage as one of the most trusted figures in American politics.

In January 2008, Obama had an 8-point edge over Clinton as the more honest and trustworthy candidate in the Democratic primary. That grew to a 23-point advantage by April of that year, according to Washington Post-ABC News polls. Later that year, the Post-ABC poll showed Obama up 8 points on Republican nominee John McCain as the more honest candidate.

Obama held such strong marks during his first term, with the public giving the new president the benefit of the doubt. Up for re-election, he went into the 2012 campaign home stretch topping Mitt Romney by 9 points on honesty in a mid-October ABC/Post poll.

But now, that carefully honed image of trustworthiness may be changing in Americans’ eyes.

A Quinnipiac University poll conducted late last month found 49 percent of people consider Obama honest and trustworthy, a dip from the organization’s last read on the matter in September 2011 when 58 percent said the same. He also has taken a hit among independents, which used to be a source of strength for him, since his second-term controversies have emerged. Now just 40 percent say he is honest and trustworthy, down from 58 percent in September 2011.

Obama has waning opportunities to turn it around. He’s halfway through his fifth year, and with midterm elections next fall, there’s no time to waste.

If he can’t convince the American people that they can trust him, he could end up damaging the legacy he has worked so hard to control and shape — and be remembered, even by those who once supported him, as the very opposite of the different type of leader he promised to be.

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EDITOR’S NOTE: Liz Sidoti is the national politics editor for The Associated Press. Follow her on Twitter: http://twitter.com/lsidoti